1. Field of the Invention
The present invention relates to an improvement in automatic breathing apparatus for underwater immersion of the semi-closed circuit type, said improvement consisting in mixing breathing gases in a controlled and optimal proportion according to depth, over a range which can extend from close to the surface of the water to relatively great depths, of up to around 150 meters.
2. Description of the Prior Art
The known automatic breathing apparatus of this kind work using a semi-closed circuit, with partial replacement of the breathing gas (He, O.sub.2) which is preprepared in varying proportions according to the depth range chosen and with re-cycling of the breathed gas through a conventional filter for elimination of carbon dioxide of the soda lime type. A typical automatic breathing apparatus for use at great depth according to the prior art, using a semi-closed circuit, is schematically illustrated in FIG. 1. As can be seen, the automatic breathing apparatus comprises a pair of gas cylinders 1, 2, for a mixture of helium and oxygen known in the field as a "Heliox" mixture. The cylinders 1 and 2 are connected to a pressure reducing valve 4 which is in turn connected, downstream, to the selector group 4A containing, at its outlet end, the "nozzles" or "holes" which condition the flow rate of the breathing gas according to the diameter of the hole itself. It should be remembered that, in this case, the pressure of the reducing valve 4 remains unchanged at all depths, and for this reason it is necessary to operate using the manual switch which changes "nozzle" or "hole", thus varying the flow rate of the gas.
The breathing gas, which passes through the chosen "hole" or "nozzle", enters the tube 5 leading to an aspiration plenum chamber or bag 6, from which a tube 7 leads to a mouthpiece 8. The mouthpiece 8 is also connected by means of a tube 9 to an expiration or discharge bag 10, which is in communication on one side with an overpressure valve 11, and on the other side with a tube 12 leading to a soda lime type carbon dioxide absorber indicated with 13. The absorber 13 communicates by way of 14 with the inspiration bag 6. The direction of flow of the gases is conditioned by no-return valves 16 and 17 and is indicated by the arrows. Finally, a by-pass device 15 is usually provided, actuated manually so as to compensate for the collapse of the "bags" 6, 10, due to increase of environmental pressure (the head of water above).